Golf ball

ABSTRACT

An object of the present invention is to provide a golf ball having excellent abrasion resistance and spin performance on driver shots. The present invention provides a golf ball having a spherical core and a cover covering the spherical core, wherein the cover contains a polyurethane, wherein the polyurethane comprises, as a constituent component, (A) a polyisocyanate component and (B) a polyol component containing (b1) a polyrotaxane, and wherein (b1) the polyrotaxane has a cyclodextrin, a linear molecule piercing through the cyclic structure of the cyclodextrin, and a blocking group located at both terminals of the linear molecule to prevent disassociation of the cyclodextrin, and at least a part of hydroxyl groups of the cyclodextrin is modified with a caprolactone chain via —O—C 3 H 6 —O— group.

FIELD OF THE INVENTION

The present invention relates to a technology for improving a cover of agolf ball, more specifically relates to a technology for improving apolyurethane cover of a golf ball.

DESCRIPTION OF THE RELATED ART

As a resin component constituting a cover of a golf ball, an ionomerresin or a polyurethane is used. The cover containing the ionomer resinis excellent in rebound, durability, processability or the like, thus iswidely used. However, the cover containing the ionomer resin has highstiffness and hardness, thus the shot feeling is poor. Furthermore, itis also pointed out that the golf ball comprising the cover containingthe ionomer resin fails to exhibit a satisfactory spin performance, andthe controllability thereof is inferior. On the other hand, it is wellknown that shot feeling and spin performance improve if the polyurethaneis used as the resin component constituting the cover, compared to theionomer resin.

For example, JP 2005-523958 A discloses a golf ball comprising a coreand a cover, the cover comprising a polyurethane elastomer, thepolyurethane elastomer comprising a reaction product of (a) aHDI-terminated prepolymer comprising a reaction product of one or morepolyols with a stoichiometric excess of HDI diisocyanate monomer whereinunreacted HDI diisocyanate monomer is removed to less than about 2 wt. %and (b) at least one hydroxyl or amine functional chain extender.

JP 2007-90065 A discloses a golf ball comprising a core and one or morecover layer covering the core, wherein at least one cover layer isformed primarily from a thermoplastic polyurethane elastomer obtained bya curing reaction of a polyurethane undiluted solution containing apolyol component and a polyisocyanate component, and wherein the polyolcomponent includes a copolymeric polycarbonate polyol.

JP 2005-28153 A discloses a multi-piece golf ball that is at leastpartially formed from a polyurethane or polyurea composition, whereinthe polyurethane or polyurea composition comprises at least onediisocyanate, at least one polyol (polyurethane) or amine-terminatedcompound (polyurea), and at least one curing agent.

JP 2009-160156 A discloses a golf ball comprising a core consisting of acenter and at least one intermediate layer covering the center; and acover covering the core, wherein the cover is formed from a covercomposition containing a thermoplastic polyurethane (A), apolyisocyanate compound (B) having two or more isocyanate groups, and apolyhydroxyether (C) as a resin component, wherein the cover compositionhas a slab hardness in a range from 20 to 55 in Shore D hardness, andthe cover has a thickness in a range from 0.1 mm to 1.5 mm. JP2009-254684 A discloses a golf ball comprising a core and a cover,wherein the cover is formed from a cover composition containing athermoplastic polyurethane (A) and a urethane prepolymer (B) having twoor more isocyanate groups as a resin component.

SUMMARY OF THE INVENTION

In general, a golf ball having a soft cover is excellent in abrasionresistance, but shows a great spin rate on driver shots, therebytraveling a short flight distance on driver shots. In other words, forthe cover of the golf ball, there is a trade-off between the spinperformance on driver shots and the abrasion resistance. A cover that isexcellent in both of these properties is desirable. The presentinvention has been made in view of the above circumstances, and anobject of the present invention is to provide a golf ball that has acover using a polyurethane as a resin component and is excellent in theabrasion resistance and the spin performance on driver shots.

The present invention that has solved the above problems provides a golfball having a spherical core and a cover covering the spherical core,wherein the cover contains a polyurethane and the polyurethanecomprises, as a constituent component, (A) a polyisocyanate componentand (B) a polyol component containing (b1) a polyrotaxane, and wherein(b1) the polyrotaxane has a cyclodextrin, a linear molecule piercingthrough the cyclic structure of the cyclodextrin, and blocking groupslocated at both terminals of the linear molecule to preventdisassociation of the cyclodextrin, and at least a part of hydroxylgroups of the cyclodextrin is modified with a caprolactone chain via—O—C₃H₆—O— group. According to the present invention, a golf ball thathas a cover using a polyurethane as a resin component and is excellentin the abrasion resistance and the spin performance on driver shots isobtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a figure illustrating a molecular structure of one example ofthe polyrotaxane used in the present invention; and

FIG. 2 is a partially cutaway sectional view showing a golf ballaccording to one embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides a golf ball having a spherical core and acover covering the spherical core, wherein the cover contains apolyurethane and the polyurethane comprises, as a constituent component,(A) a polyisocyanate component and (B) a polyol component containing(b1) a polyrotaxane, and wherein (b1) the polyrotaxane has acyclodextrin, a linear molecule piercing through the cyclic structure ofthe cyclodextrin, and blocking groups located at both terminals of thelinear molecule to prevent disassociation of the cyclodextrin, and atleast a part of hydroxyl groups of the cyclodextrin is modified with acaprolactone chain via —O—C₃H₆—O— group. It is noted that the coverconstitutes the outermost layer of the golf ball body (excluding a paintfilm).

The cover of the golf ball according to the present invention contains apolyurethane as a resin component. The polyurethane comprises, as aconstituent component, (A) a polyisocyanate component and (B) a polyolcomponent containing (b1) a polyrotaxane. The polyurethane is apolyurethane obtained by a reaction between (A) the polyisocyanatecomponent and (B) the polyol component containing (b1) the polyrotaxane,and having a plurality of urethane bonds formed in the molecule thereof.

(A) The polyisocyanate component is not particularly limited, as long asit has at least two isocyanate groups, and examples thereof include anaromatic polyisocyanate, an alicyclic polyisocyanate or aliphaticpolyisocyanate. Examples of the aromatic polyisocyanate include2,4-toluene diisocyanate, 2,6-toluene diisocyanate, a mixture of2,4-toluene diisocyanate and 2,6-toluene diisocyanate (TDI),4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate(NDI), 3,3′-bitolylene-4,4′-diisocyanate (TODD, xylylene diisocyanate(XDI), tetramethylxylylenediisocyanate (TMXDI), and para-phenylenediisocyanate (PPDI). Examples of the alicyclic polyisocyanate oraliphatic polyisocyanate include 4,4′-dicyclohexylmethane diisocyanate(H₁₂MDI), hydrogenated xylylenediisocyanate (H₆XDI), hexamethylenediisocyanate (HDI), isophorone diisocyanate (IPDI), and norbornenediisocyanate (NBDI). The polyisocyanate may be used solely or as amixture of at least two of them.

In view of improving the abrasion resistance, the aromaticpolyisocyanate is preferably used as (A) the polyisocyanate component.Use of the aromatic polyisocyanate enhances the mechanical property ofthe obtained polyurethane and provides a cover having an excellentabrasion resistance. In addition, in view of improving the weatherresistance, as (A) the polyisocyanate component, a non-yellowing typepolyisocyanate (e.g. TMXDI, XDI, HDI, H₆XDI, IPDI, H₁₂MDI and NBDI) ispreferably used, 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI) is morepreferably used. Since 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI)has a rigid structure, the mechanical property of the resultingpolyurethane is enhanced, and thus a cover having an excellent abrasionresistance is obtained.

Next, (B) the polyol component containing (b1) the polyrotaxane will beexplained. (b1) The polyrotaxane has a cyclodextrin, a linear moleculepiercing through the cyclic structure of the cyclodextrin, and blockinggroups located at both terminals of the linear molecule to preventdisassociation of the cyclodextrin. (b1) The polyrotaxane isviscoelastic, since the cyclodextrin molecule is movable along thelinear molecule that pierces through the cyclodextrin in a skeweringmanner (pulley effect). Even if a tension is applied to (b1) thepolyrotaxane, the tension can be uniformly dispersed due to the pulleyeffect. It is noted that, in the present invention, (B) the polyolcomponent is not particularly limited, as long as it has a plurality ofhydroxyl groups. (b1) The polyrotaxane is a polyol component, since aplurality of hydroxyl groups which may react with an isocyanate group,exist on the cyclodextrin cyclic structure thereof.

The cyclodextrin is a general term for an oligosaccharide having acyclic structure. The cyclodextrin is, for example, a molecule having 6to 8 D-glucopyranose residues being linked in a cyclic shape via anα-1,4-glucoside bond. Examples of the cyclodextrin includeα-cyclodextrin (number of glucose units: 6), β-cyclodextrin (number ofglucose units: 7), and γ-cyclodextrin (number of glucose units: 8), andα-cyclodextrin is preferable. As the cyclodextrin, one type may be usedsolely, and two or more types may be used in combination.

The linear molecule is not particularly limited, as long as it is alinear molecule capable of piercing through the cyclic structure of thecyclodextrin so that the cyclic structure of the cyclodextrin isrotatable around the linear molecule. Examples of the linear moleculeinclude polyalkylene, polyester, polyether, and polyacrylic acid. Amongthem, polyether is preferable, polyethylene glycol is particularlypreferable. Polyethylene glycol has less steric hindrance, and thus caneasily pierce through the cyclic structure of the cyclodextrin.

The weight average molecular weight of the linear molecule is preferably5,000 or more, more preferably 6,000 or more, and is preferably 100,000or less, more preferably 80,000 or less.

The linear molecule preferably has a functional group at both terminalsthereof. When the linear molecule has the functional group, the linearmolecule can easily react with the blocking group. Examples of thefunctional group include a hydroxyl group, carboxyl group, amino group,and thiol group.

The blocking group is not particularly limited, as long as it is locatedat both terminals of the linear molecule to prevent the cyclodextrinfrom disassociating from the linear molecule. Examples of the method forpreventing the disassociation include a method of using a bulky blockinggroup to physically prevent the disassociation, and a method of using anionic blocking group to electrostatically prevent the disassociation.Examples of the bulky blocking group include a cyclodextrin and anadamantyl group. The number of the cyclodextrins which the linearmolecule pierces through preferably ranges from 0.06 to 0.61, morepreferably ranges from 0.11 to 0.48, even more preferably ranges from0.24 to 0.41, if the maximum number of the cyclodextrins which thelinear molecule pierces through is deemed as 1. This is because if thenumber of the cyclodextrins is less than 0.06, the pulley effect may notbe exerted, and if the number of the cyclodextrins exceeds 0.61, thecyclodextrins are very densely located, so that the movability of thecyclodextrin may decrease.

(b1) The polyrotaxane used in the present invention is a polyrotaxanehaving at least a part of hydroxyl groups of the cyclodextrin beingmodified with a caprolactone chain. Modifying with the caprolactonechain enhances the compatibility of (b1) the polyrotaxane with thepolyurethane. Further, Modifying with the caprolactone chain enhancesthe flexibility of (b1) the polyrotaxane, thereby enhancing the spinperformance of the golf ball on approach shots.

As the above modification, for example, the hydroxyl groups of thecyclodextrin are treated with propylene oxide to hydroxylpropylate thecyclodextrin, and then ε-caprolactone is added to perform ring-openingpolymerization. As a result of this modification, the caprolactone chain—(CO(CH₂)₅O)nH (n is a natural number ranging from 1 to 100) is linkedto the exterior side of the cyclic structure of the cyclodextrin via—O—C₃H₆—O— group. The above “n” represents the degree of polymerization,and is preferably a natural number ranging from 1 to 100, morepreferably a natural number ranging from 2 to 70, even more preferably anatural number ranging from 3 to 40. At the other end of thecaprolactone chain, a hydroxyl group is formed through the ring-openingpolymerization.

The ratio of the hydroxyl groups modified with the caprolactone chain toall the hydroxyl groups (100 mole %) included in the cyclodextrin beforethe modification is preferably 2 mole % or more, more preferably 5 mole% or more, even more preferably 10 mole % or more. If the ratio of thehydroxyl groups modified with the caprolactone chain falls within theabove range, the flexibility of (b1) the polyrotaxane is greater, andthus the spin performance of the golf ball under a wet condition onapproach shots is further enhanced.

FIG. 1 is a figure illustrating a molecular structure of one example ofthe polyrotaxane used in the present invention. A polyrotaxane 10 has acyclodextrin 12, a linear molecule 14 piercing through the cyclicstructure of the cyclodextrin 12, and blocking groups 16 located at bothterminals of the linear molecule 14 to prevent disassociation of thecyclodextrin 12, and a caprolactone chain 18 is linked to the exteriorside of the cyclic structure of the cyclodextrin 12 via —O—C₃H₆—O— group(not shown).

The hydroxyl value of (b1) the polyrotaxane is preferably 10 mg KOH/g ormore, more preferably 15 mg KOH/g or more, even more preferably 20 mgKOH/g or more, and is preferably 400 mg KOH/g or less, more preferably300 mg KOH/g or less, even more preferably 220 mg KOH/g or less,particularly preferably 180 mg KOH/g or less. If the hydroxyl value of(b1) the polyrotaxane falls within the above range, the compatibility of(b1) the polyrotaxane with the polyurethane elastomer becomes better. Itis noted that the hydroxyl value may be measured according to JIS K1557-1, for example, by an acetylation method.

The total molecular weight of (b1) the polyrotaxane is preferably 30,000or more, more preferably 40,000 or more, even more preferably 50,000 ormore, and is preferably 3,000,000 or less, more preferably 2,500,000 orless, even more preferably 2,000,000 or less, in a weight averagemolecular weight. If the total weight average molecular weight is 30,000or more, the resultant cover composition has greater elasticity, and ifthe total weight average molecular weight is 3,000,000 or less, theresultant cover composition has greater flexibility and thus the spinperformance of the golf ball on approach shots becomes better. It isnoted that the total weight average molecular weight may be measured,for example, by gel permeation chromatography (GPC) using polystyrene asa standard substance, tetrahydrofuran as an eluant, and an organicsolvent system GPC column (e.g., “Shodex (registered trademark) KFseries” available from Showa Denko K.K.) as a column.

Specific examples of (b1) the polyrotaxane modified with thepolycaprolactone chain include SeRM (registered trademark) super polymerSH3400P, SH2400P, and SH1310P available from Advanced Softmaterials Inc.

(B) The polyol component may further contain (b2) other polyolcomponent. (b2) The other polyol component is not particularly limited,as long as it has a plurality of hydroxyl groups, and examples thereofinclude a low molecular weight polyol and a high molecular weightpolyol.

Examples of the low molecular weight polyol include a diol such asethylene glycol, diethylene glycol, triethylene glycol, propanediol(e.g. 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, andthe like), dipropylene glycol, butanediol (e.g. 1,2-butanediol,1,3-butanediol, 1,4-butanediol, 2,3-butanediol,2,3-dimethyl-2,3-butanediol, and the like), neopentyl glycol,pentanediol, hexanediol, heptanediol, octanediol,1,4-cyclohexanedimethylol, aniline diol, and bisphenol A type diol; atriol such as glycerin, trimethylolpropane, and hexanetriol, and atetraol or a hexol such as pentaerythritol and sorbitol.

Examples of the high molecular weight polyol include a polyether polyolsuch as polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), andpolyoxytetramethylene glycol (PTMG); a condensed polyester polyol suchas polyethylene adipate (PEA), polybutylene adipate (PBA), andpolyhexamethylene adipate (PNMA); a lactone polyester polyol such aspoly-ε-caprolactone (PCL), a polycarbonate polyol such aspolyhexamethylene carbonate; and an acrylic polyol.

The number average molecular weight of the high molecular weight polyol,for example, is preferably 400 or more, more preferably 1,000 or more,without particular limitation. If the number average molecular weight ofthe high molecular weight polyol is excessively small, the obtainedpolyurethane is so hard that the shot feeling of the golf ball may belowered. The upper limit of the number average molecular weight of thehigh molecular weight polyol is preferably 10,000, more preferably8,000, without particular limitation. It is noted that the numberaverage molecular weight may be measured by gel permeationchromatography (GPC), using polystyrene as a standard material,tetrahydrofuran as an eluate, and two of TSK-GEL SUPERH2500 (availablefrom Tosoh Corporation) as a column.

Examples of (B) the polyol component include an embodiment where (B) thepolyol component consists of (b1) the polyrotaxane; an embodiment where(B) the polyol component consists of (b1) the polyrotaxane and (b2) thehigh molecular weight polyol; an embodiment where (B) the polyolcomponent consists of (b1) the polyrotaxane and (b2) the low molecularweight polyol; and an embodiment where (B) the polyol component consistsof (b1) the polyrotaxane and (b2) the high molecular weight polyol andthe low molecular weight polyol. It is noted that the low molecularweight polyol and the high molecular weight polyol may be used solely oras a mixture of at least two of them.

The amount of (b1) the polyrotaxane in the polyurethane is preferably 1mass % or more, more preferably 3 mass % or more, even more preferably 7mass % or more. This is because if the amount of (b1) the polyrotaxaneis excessively low, its improvement effect in the abrasion resistance issmall. In addition, the amount of (b1) the polyrotaxane in thepolyurethane is preferably less than 50 mass %, more preferably 30 mass% or less, even more preferably 20 mass % or less. This is because ifthe amount of (b1) the polyrotaxane is excessively high, a gel may beformed during the synthesis of the polyurethane.

In the polyurethane, the constituent ratio of (A) the polyisocyanatecomponent to (B) the polyol component, i.e. the molar ratio (NCO/OH) ofthe isocyanate group (NCO) in (A) the polyisocyanate component to thehydroxyl group (OH) in (B) the polyol component is preferably 0.7 ormore, more preferably 0.8 or more, even more preferably 0.9 or more, andis preferably 1.0 or less, more preferably less than 1.0, even morepreferably 0.99 or less. In addition, when (B) the polyol componentfurther contains (b2) the other polyol component than (b1) thepolyrotaxane, the molar ratio (NCO/OH) of the isocyanate group (NCO) in(A) the polyisocyanate component to the hydroxyl group (OH) in (b2) theother polyol component is preferably 0.8 or more and 1.2 or less, andmore preferably 1.0.

The polyurethane used in the present invention may further comprise apolyamine as a constituent component, in addition to (A) thepolyisocyanate component and (B) the polyol component. The polyamine isnot particularly limited, as long as it has at least two amine groups.Examples of the polyamine include an aliphatic polyamine, an alicyclicpolyamine, and an aromatic polyamine. Examples of the aliphaticpolyamine include ethylenediamine, propylenediamine, butylenediamine,and hexamethylenediamine. Examples of the alicyclic polyamine includeisophoronediamine and piperazine.

The aromatic polyamine is not particularly limited, as long as it has atleast two amino groups directly or indirectly bonded to an aromaticring. Herein, the “indirectly bonded to an aromatic ring” means that theamino group is bonded to an aromatic ring via, for example, a loweralkylene group. The aromatic polyamine may be, for example, a monocyclicaromatic polyamine having at least two amino groups bonded to onearomatic ring, or a polycyclic aromatic polyamine having at least twoaminophenyl groups each having at least one amino group bonded to onearomatic ring.

Examples of the monocyclic aromatic polyamine include a type whereinamino groups are directly bonded to an aromatic ring, such asphenylenediamine, tolylenediamine, diethyltoluenediamine, anddimethylthiotoluenediamine, and a type wherein amino groups are bondedto an aromatic ring via a lower alkylene group, such as xylylenediamine.Further, the polycyclic aromatic polyamine may be either apoly(aminobenzene) having at least two aminophenyl groups directlybonded to each other, or a compound having at least two aminophenylgroups bonded to each other via a lower alkylene group or an alkyleneoxide group. Among them, a diaminodiphenylalkane having two aminophenylgroups bonded to each other via a lower alkylene group is preferable,4,4′-diaminodiphenylmethane and a derivative thereof are particularlypreferable.

The constitutional embodiment of the polyurethane used in the presentinvention is not particularly limited, and examples thereof include anembodiment where the polyurethane is formed from (A) the polyisocyanatecomponent and (b1) the polyrotaxane; an embodiment where thepolyurethane is formed from (A) the polyisocyanate component, (b1) thepolyrotaxane and (b2) the high molecular weight polyol component; and anembodiment where the polyurethane is formed from (A) the polyisocyanatecomponent, (b1) the polyrotaxane, and (b2) the high molecular weightpolyol component and the low molecular weight polyol component.

The polyurethane may be either a thermoplastic polyurethane or athermosetting polyurethane. The thermoplastic polyurethane is apolyurethane exhibiting plasticity by heating and generally means apolyurethane having a linear chain structure of a high-molecular weightto a certain extent. The thermosetting polyurethane is a polyurethaneobtained through a curing reaction between a relatively low molecularweight prepolymer and a curing agent when using. By controlling thenumber of the functional group of the prepolymer or the curing agent tobe used, a thermosetting polyurethane having a three-dimensionalcrosslinked structure is obtained. As the polyurethane used in thepresent invention, a thermoplastic polyurethane is preferred. This isbecause if the thermoplastic polyurethane is used, the cover can beeasily molded.

Examples of the method for synthesizing the polyurethane used in thepresent invention include a one-shot method and a prepolymer method. Theone-shot method is a method of reacting a polyisocyanate component and apolyol component or the like at one time. The prepolymer method is amethod of reacting a polyisocyanate component and a polyol component orthe like in multiple steps, e.g. a method of synthesizing a urethaneprepolymer having a relatively low molecular weight, followed by furtherpolymerization to have a higher molecular weight.

Next, the method for synthesizing the polyurethane used in the presentinvention by the one-shot method will be described. In the one-shotmethod, the polyurethane is synthesized by reacting (A) thepolyisocyanate component and (B) the polyol component containing (b1)the polyrotaxane.

The temperature at which the synthesis reaction of the polyurethane iscarried out is preferably 10° C. or more, more preferably 30° C. ormore, even more preferably 50° C. or more, and is preferably 200° C. orless, more preferably 150° C. or less, even more preferably 100° C. orless. In addition, the reaction time for the synthesis reaction of thepolyurethane is preferably 10 minutes or more, more preferably 1 hour ormore, even more preferably 3 hours or more, and is preferably 32 hoursor less, more preferably 16 hours or less, even more preferably 8 hoursor less.

The synthesis reaction of the polyurethane is preferably conducted in anatmosphere of dry nitrogen.

In synthesizing the polyurethane, a publicly known catalyst may be used.Examples of the catalyst include a monoamine such as triethylamine andN,N-dimethylcyclohexylamine; a polyamine such asN,N,N′,N′-tetramethylethylene diamine andN,N,N′,N″,N″-pentamethyldiethylene triamine; a cyclic diamine such as1,8-diazabicyclo-[5.4.0]-7-undecene (DBU) and triethylenediamine; and atin-based catalyst such as dibutyl tin dilaurylate and dibutyl tindiacetate. These catalysts may be used solely, or two or more of thesecatalysts may be used in combination. Among them, the tin-based catalystsuch as dibutyl tin dilaurylate and dibutyl tin diacetate is preferable,and in particular, dibutyl tin dilaurylate is preferably used.

The cover of the golf ball according to the present invention is formedfrom a cover composition containing the above polyurethane as a resincomponent. The cover composition may further contain another resincomponent, as long as it does not impair the inventive effect. Examplesof another resin component include an ionomer resin and a thermoplasticelastomer. The ionomer resin includes, for example, a product preparedby neutralizing at least a part of carboxyl groups in a binary copolymercomposed of ethylene and an α,β-unsaturated carboxylic acid having 3 to8 carbon atoms with a metal ion; a product prepared by neutralizing atleast a part of carboxyl groups in a ternary copolymer composed ofethylene, an α,β-unsaturated carboxylic acid having 3 to 8 carbon atomsand an α,β-unsaturated carboxylic acid ester with a metal ion, or amixture of those. Specific examples of the ionomer resin include“Himilan (registered trademark)” available from Du Pont-MitsuiPolychemicals Co., Ltd., “Surlyn (registered trademark)” available fromE.I. du Pont de Nemours and Company, and “Iotek (registered trademark)”available from ExxonMobil Chemical Corporation. Specific examples of thethermoplastic elastomer include a thermoplastic polyurethane elastomerhaving a trade name of “Elastollan (registered trademark) (e.g,“Elastollan XNY88A”)” available from BASF Japan Ltd., a thermoplasticpolyamide elastomer having a trade name of “Pebax (registered trademark)(e.g. “Pebax 2533”)” available from Arkema K. K.; a thermoplasticpolyester elastomer having a trade name of “Hytrel (registeredtrademark) (e.g. “Hytrel 3548”, “Hytrel 4047”)” available from DuPont-Toray Co., Ltd.; and a thermoplastic polystyrene elastomer having atrade name of “Rabalon (registered trademark)” available from MitsubishiChemical Corporation.

In the case that another resin component is used as the resin componentconstituting the cover composition, the amount of the above polyurethanein the total resin component is preferably 85 mass % or more, morepreferably 90 mass % or more, even more preferably 95 mass % or more.The resin component may consist of the above polyurethane.

The cover composition may further contain a pigment component such astitanium oxide, a blue pigment or the like; a weight adjusting agentsuch as calcium carbonate, barium sulfate or the like; a dispersant; anantioxidant; an ultraviolet absorber; a light stabilizer; a fluorescentmaterial or a fluorescent brightener; and the like, as long as they donot impair the performance of the cover.

The amount of the white pigment (e.g. titanium oxide) is preferably 0.5part by mass or more, more preferably 1 part by mass or more, and ispreferably 10 parts by mass or less, more preferably 8 parts by mass orless, with respect to 100 parts by mass of the resin componentconstituting the cover. If the amount of the white pigment is 0.5 partby mass or more, it is possible to impart the opacity to the cover.Further, if the amount of the white pigment exceeds 10 parts by mass,the durability of the obtained cover may deteriorate.

The loss modulus of elasticity E″ of the cover is preferably 4.5×10⁷ Paor less, more preferably 4.2×10⁷ Pa or less, even more preferably4.0×10⁷ Pa or less, and is preferably 8.0×10⁶ Pa or more, morepreferably 9.0×10⁶ Pa or more, even more preferably 9.5×10⁶ Pa or more.If the loss modulus of elasticity E″ of the cover is 8.0×10⁶ Pa or more,the spin rate on driver shots is further lowered, and if the lossmodulus of elasticity E″ of the cover is 4.5×10⁷ Pa or less, the spinrate on approach shots is further increased. The method for measuringthe loss modulus of elasticity of the cover will be described later.

The pencil hardness of the cover is preferably H or more, morepreferably 2H or more, even more preferably 3H or more, and ispreferably 9H or less, more preferably 8H or less, even more preferably7H or less. If the pencil hardness of the cover is H or more, the spinrate on driver shots is further lowered, and if the pencil hardness ofthe cover is 9H or less, the spin rate on approach shots is furtherincreased. The method for measuring the pencil hardness of the coverwill be described later.

The slab hardness of the cover composition is preferably 74 or more,more preferably 76 or more, even more preferably 78 or more, and ispreferably 94 or less, more preferably 92 or less, even more preferably90 or less in Shore A hardness. If the slab hardness of the covercomposition is 74 or more in Shore A hardness, the spin rate on drivershots is further lowered, and if the slab hardness of the covercomposition is 94 or less in Shore A hardness, the spin rate on approachshots is further increased.

The cover composition may be obtained, for example, by dry blending theabove polyurethane and the additives that are blended where necessary.Further, the dry blended mixture may be extruded into a pellet form. Inthe dry blending, for example, a mixer capable of blending raw materialsin a pellet form is preferably used, a tumbler type mixer is morepreferably used. The extrusion can be carried out using a publicly knownextruder such as a single-screw extruder, a twin-screw extruder, and atwin-screw/single-screw extruder.

[Golf Ball]

The construction of the golf ball of the present invention is notparticularly limited, as long as it is a golf ball comprising aspherical core and a cover covering the spherical core. Examples of theconstruction of the golf ball include a two-piece golf ball having asingle layered spherical core and a cover covering the spherical core; athree-piece golf ball having a spherical core composed of a center and asingle layered intermediate layer covering the center, and a covercovering the spherical core; a multi-piece golf ball having a sphericalcore composed of a center and two or more intermediate layers coveringthe center, and a cover covering the spherical core; and the like.

The core or center may employ a conventionally known rubber composition(hereinafter simply referred to as “core rubber composition”occasionally), and may be formed by heat pressing, for example, a rubbercomposition containing a base rubber, a co-crosslinking agent and acrosslinking initiator.

As the base rubber, particularly preferred is a high cis-polybutadienehaving a cis-bond in a proportion of 40 mass % or more, more preferably70 mass % or more, and even more preferably 90 mass % or more in view ofits superior resilience. As the co-crosslinking agent, anα,β-unsaturated carboxylic acid having 3 to 8 carbon atoms or a metalsalt thereof is preferable, and a metal salt of acrylic acid or a metalsalt of methacrylic acid is more preferable. As the metal constitutingthe metal salt, zinc, magnesium, calcium, aluminum or sodium ispreferable, and zinc is more preferable. The amount of theco-crosslinking agent is preferably 20 parts by mass or more and 50parts by mass or less with respect to 100 parts by mass of the baserubber. In the case that the α,β-unsaturated carboxylic acid having 3 to8 carbon atoms is used as the co-crosslinking agent, a metal compound(e.g. magnesium oxide) is preferably used. As the crosslinkinginitiator, an organic peroxide is preferably used. Specific examples ofthe organic peroxide include dicumyl peroxide,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide. Amongthem, dicumyl peroxide is preferably used. The amount of thecrosslinking initiator is preferably 0.2 part by mass or more, morepreferably 0.3 part by mass or more, and is preferably 5 parts by massor less, more preferably 3 parts by mass or less, with respect to 100parts by mass of the base rubber.

In addition, the core rubber composition may further contain an organicsulfur compound. As the organic sulfur compound, diphenyl disulfides,thiophenols or thionaphthols are preferably used. The amount of theorganic sulfur compound is preferably 0.1 part by mass or more, morepreferably 0.3 part by mass or more, and is preferably 5.0 parts by massor less, more preferably 3.0 parts by mass or less, with respect to 100parts by mass of the base rubber. The core rubber composition mayfurther contain a carboxylic acid and/or a salt thereof. As thecarboxylic acid and/or the salt thereof, a carboxylic acid having 1 to30 carbon atoms and/or a salt thereof is preferred. As the carboxylicacid, an aliphatic carboxylic acid or an aromatic carboxylic acid (e.g.benzoic acid) may be used. The amount of the carboxylic acid and/or thesalt thereof is preferably 1 part by mass or more and 40 parts by massor less with respect to 100 parts by mass of the base rubber.

The core rubber composition may further contain a weight adjusting agentsuch as zinc oxide and barium sulfate, an antioxidant, or a coloredpowder, in addition to the base rubber, the co-crosslinking agent, thecrosslinking initiator, and the organic sulfur compound. The moldingconditions for heat pressing the core rubber composition may bedetermined appropriately depending on the rubber formulation. Generally,the heat pressing is preferably carried out at 130° C. to 200° C. for 10to 60 minutes, or carried out in a two-step heating of heating at 130°C. to 150° C. for 20 to 40 minutes followed by heating at 160° C. to180° C. for 5 to 15 minutes.

In the case that the spherical core has an intermediate layer, examplesof the intermediate layer material include a thermoplastic resin such asa polyurethane resin, an ionomer resin, a polyamide resin, andpolyethylene; a thermoplastic elastomer such as a styrene elastomer, apolyolefin elastomer, a polyurethane elastomer, a polyamide elastomer,and a polyester elastomer; and a cured product of a rubber composition.Herein, examples of the ionomer resin include a product prepared byneutralizing at least a part of carboxyl groups in a binary copolymercomposed of ethylene and an α,β-unsaturated carboxylic acid with a metalion; and a product prepared by neutralizing at least a part of carboxylgroups in a ternary copolymer composed of ethylene, an α,β-unsaturatedcarboxylic acid and an α,β-unsaturated carboxylic acid ester with ametal ion. The intermediate layer may further contain a weight adjustingagent such as barium sulfate and tungsten, an antioxidant, and apigment.

The method for forming the intermediate layer is not particularlylimited, and examples thereof include a method which comprises moldingthe intermediate layer composition into hemispherical half shells inadvance, covering the spherical body with two of the half shells, andsubjecting the spherical body with two of the half shells to thecompression molding; and a method which comprises injection molding theintermediate layer composition directly onto the spherical body so as tocover the spherical body.

In case of injection molding the intermediate layer composition onto thespherical body to form the intermediate layer, it is preferred to useupper and lower molds, each having a hemispherical cavity, for formingthe intermediate layer. When molding the intermediate layer by theinjection molding, the hold pin is protruded to hold the spherical body,and the heated and melted intermediate layer composition is charged andthen cooled to obtain the intermediate layer.

When molding the intermediate layer in the compression molding method,molding of the half shell may be conducted by either a compressionmolding method or an injection molding method, and the compressionmolding method is preferable. The compression molding of theintermediate layer composition into the half shell can be carried out,for example, under a pressure of 1 MPa or more and 20 MPa or less at atemperature of −20° C. or more and 70° C. or less relative to the flowbeginning temperature of the intermediate layer composition. Byperforming the molding under the above conditions, a half shell having auniform thickness can be formed. Examples of the method for molding theintermediate layer using half shells include a method of covering thespherical body with two of the half shells and then subjecting thespherical core with two of the half shells to the compression molding.The compression molding of the half shells into the intermediate layercan be carried out, for example, under a pressure of 0.5 MPa or more and25 MPa or less at a temperature of −20° C. or more and 70° C. or lessrelative to the flow beginning temperature of the intermediate layercomposition. By performing the molding under the above conditions, anintermediate layer having a uniform thickness can be formed.

It is noted that the molding temperature means the highest temperaturewhere the temperature at the surface of the concave portion of the lowermold reaches from closing the mold to opening the mold. In addition, theflow beginning temperature of the composition may be measured using thethermoplastic resin composition in a pellet form under the followingconditions with “Flow Tester CFT-500” available from ShimadzuCorporation.

Measuring conditions: plunger area: 1 cm², die length: 1 mm, diediameter: 1 mm, load: 588.399 N, starting temperature: 30° C., andtemperature increase rate: 3° C./min.

The center hardness Ho of the spherical core is preferably 40 or more,more preferably 45 or more, and even more preferably 50 or more in ShoreC hardness. If the center hardness Ho of the spherical core is less than40 in Shore C hardness, the spherical core becomes so soft that theresilience thereof may be lowered. In addition, the center hardness Hoof the spherical core is preferably 70 or less, more preferably 65 orless, and even more preferably 60 or less in Shore C hardness. If thecenter hardness Ho exceeds 70 in Shore C hardness, the spherical corebecomes so hard that the shot feeling thereof may be lowered.

The surface hardness Hs of the spherical core is preferably 65 or more,more preferably 70 or more, even more preferably 75 or more, and ispreferably 100 or less, more preferably 95 or less, even more preferably90 or less in Shore C hardness. If the surface hardness of the sphericalcore is 65 or more in Shore C hardness, the spherical core does notbecome excessively soft, and thus a better resilience is obtained. Inaddition, if the surface hardness of the spherical core is 100 or lessin Shore C hardness, the spherical core does not become excessivelyhard, and thus a better shot feeling is obtained.

The hardness difference (Hs−Ho) between the surface hardness Hs and thecenter hardness Ho of the spherical core is preferably 10 or more, morepreferably 12 or more, even more preferably 15 or more, and ispreferably 40 or less, more preferably 35 or less, even more preferably30 or less in Shore C hardness. If the hardness difference between thecore surface and the core center is great, the obtained golf ball has ahigher launch angle and a lower spin rate on driver shots, and thustravels a greater flight distance.

The spherical core preferably has a diameter of 34.8 mm or more, morepreferably 36.8 mm or more, even more preferably 38.8 mm or more, andpreferably has a diameter of 42.2 mm or less, more preferably 41.8 mm orless, even more preferably 41.2 mm or less, most preferably 40.8 mm orless. If the spherical core has a diameter of 34.8 mm or more, thethickness of the cover does not become too thick and thus the resiliencebecomes better. On the other hand, if the spherical core has a diameterof 42.2 mm or less, the thickness of the cover does not become too thinand thus the cover functions better.

When the spherical core has a diameter in a range from 34.8 mm to 42.2mm, the compression deformation amount of the spherical core (shrinkingamount of the spherical core along the compression direction) whenapplying a load from 98 N as an initial load to 1275 N as a final loadto the spherical core is preferably 2.0 mm or more, more preferably 2.8mm or more, and is preferably 6.0 mm or less, more preferably 5.0 mm orless, even more preferably 4.5 mm or less. If the compressiondeformation amount is 2.0 mm or more, the shot feeling becomes better,and if the compression deformation amount is 6.0 mm or less, theresilience becomes higher.

The embodiment for molding the cover composition into the coverincludes, without any limitation, an embodiment which comprisesinjection molding the cover composition directly onto the sphericalcore, and an embodiment which comprises molding the cover compositioninto a hollow-shell, covering the spherical core with a plurality of thehollow-shells and subjecting the spherical core with a plurality of thehollow shells to the compression molding (preferably an embodiment whichcomprises molding the cover composition into a half hollow-shell,covering the spherical core with two of the half hollow-shells, andsubjecting the spherical core with two of the half hollow-shells to thecompression molding). The golf ball body having the cover formed thereonis ejected from the mold, and is preferably subjected to surfacetreatments such as deburring, cleaning and sandblast where necessary. Inaddition, if desired, a mark may be formed.

The thickness of the cover is preferably 0.3 mm or more, more preferably0.4 mm or more, even more preferably 0.5 mm or more, and is preferably2.0 mm or less, more preferably 1.5 mm or less, even more preferably 1.0mm or less. If the thickness of the cover is 0.3 mm or more, the coveris easily molded, and if the thickness of the cover is 2.0 mm or less,the resilience performance of the golf ball becomes better since thecore has a relatively large diameter.

The total number of dimples formed on the cover is preferably 200 ormore and 500 or less. If the total number is less than 200, the dimpleeffect is hardly obtained. On the other hand, if the total numberexceeds 500, the dimple effect is hardly obtained because the size ofthe respective dimples is small. The shape (shape in a plan view) ofdimples includes, for example, without limitation, a circle, a polygonalshape such as a roughly triangular shape, a roughly quadrangular shape,a roughly pentagonal shape, a roughly hexagonal shape, and otherirregular shape. The shape of dimples is employed solely or at least twoof them may be used in combination.

The golf ball body having the cover formed thereon is ejected from themold, and is preferably subjected to surface treatments such asdeburring, cleaning and sandblast where necessary. In addition, ifdesired, a paint film or a mark may be formed. The paint film preferablyhas a thickness of, but is not particularly limited to, 5 μm or more,more preferably 7 μm or more, and preferably has a thickness of 50 μm orless, more preferably 40 μm or less, even more preferably 30 μm or less.If the thickness of the paint film is less than 5 μm, the paint film iseasy to wear off due to the continued use of the golf ball, and if thethickness of the paint film exceeds 50 μm, the dimple effect is reducedand thus the flight performance of the golf ball may be lowered.

The golf ball of the present invention preferably has a diameter rangingfrom 40 mm to 45 mm. In light of satisfying a regulation of US GolfAssociation (USGA), the diameter is particularly preferably 42.67 mm ormore. In light of prevention of air resistance, the diameter is morepreferably 44 mm or less, particularly preferably 42.80 mm or less. Inaddition, the golf ball of the present invention preferably has a massof 40 g or more and 50 g or less. In light of obtaining greater inertia,the mass is more preferably 44 g or more, particularly preferably 45.00g or more. In light of satisfying a regulation of USGA, the mass isparticularly preferably 45.93 g or less.

When the golf ball of the present invention has a diameter in a rangefrom 40 mm to 45 mm, the compression deformation amount of the golf ball(shrinking amount of the golf ball along the compression direction) whenapplying a load from 98 N as an initial load to 1275 N as a final loadto the golf ball is preferably 2.0 mm or more, more preferably 2.4 mm ormore, even more preferably 2.5 mm or more, most preferably 2.8 mm ormore, and is preferably 5.0 mm or less, more preferably 4.5 mm or less.If the compression deformation amount is 2.0 mm or more, the golf balldoes not become excessively hard, and thus the shot feeling thereofbecomes better. On the other hand, if the compression deformation amountis 5.0 mm or less, the resilience of the golf ball becomes higher.

FIG. 2 is a partially cutaway sectional view showing a golf ball 1according to an embodiment of the present invention. The golf ball 1comprises a spherical core 2, and a cover 3 disposed outside thespherical core 2. A plurality of dimples 31 are formed on the surface ofthe cover 3. Other portion than the dimples 31 on the surface of thecover 3 is a land 32. The cover 3 is formed from the above-mentionedcover composition.

Examples

Next, the present invention will be described in detail by way ofexamples. However, the present invention is not limited to the examplesdescribed below. Various changes and modifications without departingfrom the spirit of the present invention are included in the scope ofthe present invention.

[Evaluation Methods] (1) Compression Deformation Amount (mm)

A compression deformation amount of the core (a shrinking amount of thecore along the compression direction), when applying a load from aninitial load of 98 N to a final load of 1275 N to the core, wasmeasured.

(2) Core Hardness (Shore C Hardness)

The hardness measured on the surface of the core was adopted as thesurface hardness of the core. In addition, the hardness measured at thecentral point of a cut plane which was obtained by cutting the core intotwo hemispheres, was adopted as the center hardness of the core. Thehardness was measured with an automatic hardness tester (Digitest II,available from Bareiss company) using a testing device of “Shore C”.

(3) Slab Hardness (Shore A Hardness)

Sheets with a thickness of about 2 mm were produced by injection moldingthe cover composition. The sheets were stored at 23° C. for two weeks.At least three of these sheets were stacked on one another so as not tobe affected by the measuring substrate on which the sheets were placed,and the hardness of the stack was measured with an automatic hardnesstester (Digitest II, available from Bareiss company) using a testingdevice of “Shore A”.

(4) Pencil Hardness

A sheet with a thickness of 2 mm, a width of 2 cm and a length of 5 cmwas produced by injection molding the cover composition. The pencilhardness of the sheet was measure according to JIS K 5600-5-4.

(5) Measurement of Loss Modulus of Elasticity E″ (Pa)

The loss modulus of elasticity E″ (Pa) of the cover composition wasmeasured under the following conditions.

Apparatus: a dynamic viscoelasticity analyzer “Rheogel-E4000” availablefrom UBM Co., Ltd.

Testing sample: a sheet with a thickness of 0.5 mm was produced by heatpressing the cover composition, and a test piece was cut out from thesheet such that the test piece has a width of 4 mm and a length betweenthe clamps of 20 mm.

Measuring mode: tensile mode

Measuring temperature: 0° C.

Oscillation frequency: 10 Hz

Measuring strain: 0.05%

(6) Abrasion Resistance

A commercially available sand wedge (Trade name: NewBread Tour Forged,Shaft hardness: S, available from Sumitomo Rubber Industries, Ltd.) wasinstalled on a swing robot available from Golf Laboratories, Inc., andeach golf ball was hit at a head speed of 36 m/sec. Each hit area of thegolf ball was observed, and the abrasion resistance was evaluatedaccording to the following four grade scoring standard. It is noted thata lower score indicates a higher abrasion resistance.

Scoring Standard

0: Nearly no scratch occurred on the surface of the golf ball.1: Only a little scratch occurred on the surface of the golf ball.2: The surface of the golf ball was slightly shaved, and fuzz occurredthereon.3: The surface of the golf ball was shaved, and fuzz remarkably occurredthereon.

(7) Spin Rate on Driver Shots

A driver provided with a titanium head (Trade name: SRIXON Z745, Loftangel: 8.5°, available from Dunlop Sports Limited) was installed on aswing robot M/C available from True Temper Sports, Inc. The golf ballwas hit at a head speed of 50 m/sec, and the spin rate of the golf ballright after the hitting was measured. The measurement was conducted tentimes for each golf ball, and the average value thereof was adopted asthe measurement value of the golf ball. It is noted that the spin rateof the golf ball right after the hitting was measured by continuouslytaking a sequence of photographs of the hit golf ball.

(8) Moldability

A half shell (thickness: 0.5 mm) was produced by compression molding thecover composition, and a broken or missing part in the half shell whenejecting the half shell from the mold was visually evaluated. Thecompression molding was conducted under the conditions of a moldingtemperature of 170° C., a molding time of 5 minutes and a moldingpressure of 2.94 MPa. The case that neither broken nor missing part wasfound in the produced half shell was evaluated as “G (good)”, and thecase that a broken or missing part was found in the produced half shellwas evaluated as “P (poor)”.

[Synthesis of Polyurethane]

TABLE 1 Golf ball No. 1 2 3 4 5 6 7 Cover (A) Polyisocyanate: H₁₂MDI 304288 256 314 297 264 320 composition (A) Polyisocyanate: MDI — — — — — —— (b1) Polyrotaxane 50 100 200 50 100 200 50 (b2) High molecular weightpolyol 579 549 488 565 535 476 556 (b2) Low molecular weight polyol 6763 56 71 68 60 74 Molar ratio NCO/OH (A/b2) 1 1 1 1 1 1 1 Molar ratioNCO/OH (A/(b1 + b2)) 0.97 0.94 0.88 0.97 0.94 0.88 0.97 Amount of (b1)polyrotaxane in 5 10 20 5 10 20 5 polyurethane (mass %) Titanium oxide(amount with respect to 4 4 4 4 4 4 4 100 parts by mass of resincomponent) Physical Slab hardness of cover composition 82 82 82 84 84 8488 properties (Shore A) Loss modulus of elasticity E″ of cover 2.97 1.261.01 3.62 2.01 1.74 4.10 composition (×10⁷ Pa) Pencil hardness of covercomposition 7H 9H 9H 5H 6H 6H 2H Evaluation Moldability of cover G G G GG G G Abrasion resistance 0 0 0 1 1 1 2 Spin performance on driver shots(rpm) 2270 2290 2300 2230 2240 2240 2050 Golf ball No. 8 9 10 11 12 13Cover (A) Polyisocyanate: H₁₂MDI 303 270 — — — 160 composition (A)Polyisocyanate: MDI — — 339 321 286 — (b1) Polyrotaxane 100 200 50 100200 500 (b2) High molecular weight polyol 527 468 522 495 440 305 (b2)Low molecular weight polyol 70 62 89 84 74 35 Molar ratio NCO/OH (A/b2)1 1 1 1 1 1 Molar ratio NCO/OH (A/(b1 + b2)) 0.94 0.89 0.98 0.95 0.890.64 Amount of (b1) polyrotaxane in 10 20 5 10 20 50 polyurethane (mass%) Titanium oxide (amount with respect to 4 4 4 4 4 4 100 parts by massof resin component) Physical Slab hardness of cover composition 88 88 9090 90 — properties (Shore A) Loss modulus of elasticity E″ of cover 2.522.18 1.01 0.88 0.75 — composition (×10⁷ Pa) Pencil hardness of covercomposition 4H 5H H 2H 3H — Evaluation Moldability of cover G G G G GGel was formed Abrasion resistance 1 1 2 2 2 — Spin performance ondriver shots (rpm) 2065 2070 2315 2320 2330 — *) Amount of (A), (b1),(b2) is shown by “parts by mass”, respectively.

The polyurethane was synthesized as follows according to theformulations shown in Table 1. The polyrotaxane, polyoxytetramethyleneglycol and 1,4-butanediol were weighed by a determined amount, addedinto a steel container, and heated at 105° C. for three hours under anairtight condition. Then, a stirring rod and a temperature sensor wereinstalled in the steel container, and stirring was carried out at 200rpm. The polyisocyanate in a determined amount was added therein, andthe stirring was continued until the temperature of the temperaturesensor reached 130° C. After the temperature reached 130° C., thereaction product was immediately poured into a mold made of Teflon(registered trademark). An annealing treatment of the reaction productwas carried out at 100° C. for 15 hours in a state of being poured intothe mold made of Teflon (registered trademark). After the annealingtreatment, the cured sample was finely pulverized.

(A) Polyisocyanate: 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI)

(A) Polyisocyanate: diphenylmethane diisocyanate (MDI)

(b1) Polyrotaxane: “SeRM (registered trademark) super polymer SH2400P (apolyrotaxane having a cyclodextrin, at least a part of hydroxyl groupsof the cyclodextrin being modified with a caprolactone chain via—O—C₃H₆—O— group, a linear molecule of polyethylene glycol and ablocking group of an adamantyl group; molecular weight of linearmolecule: 20,000; hydroxyl value of polyrotaxane: 76 mg KOH/g; totalmolecular weight of polyrotaxane: 400,000 in weight average molecularweight)” available from Advanced Softmaterials Inc.

(b2) High molecular weight polyol: mixture of PTMG 1000(polyoxytetramethylene glycol having number average molecular weight of1000) and PTMG 2000 (polyoxytetramethylene glycol having number averagemolecular weight of 2000) in a ratio of PTMG 1000:PTMG 2000=6:4 (b2) Lowmolecular weight polyol: butanediol

[Production of Golf Ball] (1) Production of Core

The center rubber composition having the formulation shown in Table 2was kneaded, and heat pressed in upper and lower molds, each having ahemispherical cavity, at 170° C. for 15 minutes to obtain a sphericalcenter (diameter: 38.5 mm). Then, the intermediate layer material havingthe formulation shown in Table 2 was extruded with a twin-screw kneadingextruder to prepare an intermediate layer composition in a pellet form.The extruding conditions of the intermediate layer composition were ascrew diameter of 45 mm, a screw rotational speed of 200 rpm, and screwL/D=35, and the mixture was heated to 150 to 230° C. at the die positionof the extruder. The obtained intermediate layer composition wasinjection molded onto the center obtained above to produce a sphericalcore (diameter: 41.7 mm) having a center and an intermediate layercovering the center.

TABLE 2 Spherical core Center Formulation Polybutadiene rubber 100(parts by mass) Zinc acrylate 38 Zinc oxide 5 Diphenyl disulfide 0.5Dicumyl peroxide 1 Diameter (mm) 38.5 Intermediate Formulation Himilan1605 50 layer (parts by mass) Himilan AM7329 50 Slab hardness (Shore D)64 Thickness (mm) 1.6 Physical Diameter (mm) 41.7 properties Surfacehardness (Shore C) 98 Center hardness (Shore C) 65 Hardness difference(surface hardness - 33 center hardness) (Shore C) Compressiondeformation amount (mm) 2.55 Polybutadiene rubber: “BR730 (highcis-polybutadiene)” available from JSR Corporation Zinc acrylate:“ZNDA-90S” available from Nisshoku Techno Fine Chemical Co., Ltd. Zincoxide: “Ginrei R” available from Toho Zinc Co., Ltd. Diphenyl disulfide:available from Sumitomo Seika Chemicals Co., Ltd. Dicumyl peroxide:“Percumyl (register trademark) D” available from NOF Corporation Himilan(registered trademark) 1605: sodium ion neutralized ethylene-methacrylicacid copolymer ionomer resin available from Du Pont-Mitsui PolychemicalsCo., Ltd. Himilan AM7329: zinc ion neutralized ethylene-methacrylic acidcopolymer ionomer resin available from Du Pont-Mitsui Polychemicals Co.,Ltd.

(2) Molding of Half Shells

The polyurethane synthesized according to the formulation shown in Table1 and titanium oxide were dry blended and mixed with a twin-screwkneading extruder to prepare the cover composition in a pellet form,according to the formulation shown in Table 1. A polyurethane andtitanium oxide were dry blended and mixed with a twin-screw kneadingextruder to prepare the cover composition in a pellet form, according tothe formulation shown in Table 3. The extruding conditions of the covercomposition were a screw diameter of 45 mm, a screw rotational speed of200 rpm, and screw L/D=35, and the mixture was heated to 150 to 230° C.at the die position of the extruder. The compression molding of halfshells was conducted by charging the obtained cover composition in thepellet form one by one into each of the depressed part of the lower moldof the mold for molding half shells, and applying pressure to mold thehalf shells. The compression molding was conducted under the conditionsof a molding temperature of 170° C., a molding time of 5 minutes and amolding pressure of 2.94 MPa.

TABLE 3 Golf ball No. 14 15 16 17 18 19 Cover Elastollan XNY80A 100 — —— — — composition Elastollan XNY82A — 100 — — — — Elastollan XNY84A — —100 — 100 — Elastollan XNY88A — — — 100 — — Elastollan 1190ATR — — — — —100 Polyrotaxane — — — — 10 — Titanium oxide 4 4 4 4 4 4 Physical Slabhardness of cover composition 80 82 84 88 84 90 properties (Shore A)Loss modulus of elasticity of cover 1.43 2.72 3.91 4.50 4.09 1.26composition E″ (×10⁷ Pa) Pencil hardness of cover composition 5H 5H 3HHB 3H HB Evaluation Moldability of cover G G G G G G Abrasion resistance1 1 2 3 2 3 Spin performance on driver shots 2340 2300 2240 2070 22202330 Formulation: parts by mass

The raw materials used in Table 3 are shown below.

Elastollan (registered trademark) XNY80A: H₁₂MDI based polyurethaneelastomer (Shore A hardness: 80) available from BASF Japan Ltd.

Elastollan XNY82A: H₁₂MDI based polyurethane elastomer (Shore Ahardness: 82) available from BASF Japan Ltd.

Elastollan XNY84A: H₁₂MDI based polyurethane elastomer (Shore Ahardness: 84) available from BASF Japan Ltd.

Elastollan XNY88A: H₁₂MDI based polyurethane elastomer (Shore Ahardness: 88) available from BASF Japan Ltd.

Elastollan 1190ATR: MDI based polyurethane elastomer (Shore A hardness:90) available from BASF Japan Ltd.

(3) Molding of Cover

The core obtained in (1) was concentrically covered with two of the halfshells obtained in (2), and the core and two of the half shells werecompression molded to form the cover. The compression molding wasconducted under the conditions of a molding temperature of 145° C., amolding time of 2 minutes and a molding pressure of 9.8 MPa. The surfaceof the obtained golf ball body was subjected to a sandblast treatment,and a mark was formed thereon. Then, a clear paint was applied to thegolf ball body, and the paint was dried in an oven of 40° C. to obtain agolf ball having a diameter of 42.7 mm and a mass of 45.3 g. Evaluationresults regarding the abrasion resistance and spin performance of theobtained golf balls are shown in Tables 1 and 3.

It is apparent from Table 1 that the golf ball according to the presentinvention has excellent abrasion resistance and spin performance ondriver shots. The golf ball according to the present invention is a golfball having a spherical core and a cover covering the spherical core,wherein the cover contains a polyurethane and the polyurethanecomprises, as a constituent component, (A) a polyisocyanate componentand (B) a polyol component containing (b1) a polyrotaxane, and wherein(b1) the polyrotaxane has a cyclodextrin, a linear molecule piercingthrough the cyclic structure of the cyclodextrin, and blocking groupslocated at both terminals of the linear molecule to preventdisassociation of the cyclodextrin, and at least a part of hydroxylgroups of the cyclodextrin is modified with a caprolactone chain via—O—C₃H₆—O— group.

The golf ball No. 18 in Table 3 is the case that a mixture of thepolyrotaxane and a polyurethane was used for the cover. It is apparentthat the golf ball according to the present invention that uses apolyurethane having the polyrotaxane introduced into the moleculethereof has better abrasion resistance than the golf ball No. 18 thatuses a mixture of the polyrotaxane and a polyurethane.

This application is based on Japanese patent application No.2016-104567, filed on May 25, 2016, the content of which is herebyincorporated by reference.

1. A golf ball having a spherical core and a cover covering thespherical core, wherein the cover contains a polyurethane and thepolyurethane comprises, as a constituent component, (A) a polyisocyanatecomponent and (B) a polyol component containing (b1) a polyrotaxane, andwherein (b1) the polyrotaxane has a cyclodextrin, a linear moleculepiercing through the cyclic structure of the cyclodextrin, and blockinggroups located at both terminals of the linear molecule to preventdisassociation of the cyclodextrin, and at least a part of hydroxylgroups of the cyclodextrin is modified with a caprolactone chain via—O—C₃H₆—O— group.
 2. The golf ball according to claim 1, wherein thelinear molecule of (b1) the polyrotaxane is polyethylene glycol, and theblocking group of (b1) the polyrotaxane is an adamantyl group.
 3. Thegolf ball according to claim 1, wherein the polyurethane contains (b1)the polyrotaxane component in an amount of less than 50 mass %.
 4. Thegolf ball according to claim 1, wherein (A) the polyisocyanate componentis 4,4′-dicyclohexylmethane diisocyanate.
 5. The golf ball according toclaim 1, wherein the cover has a loss modulus of elasticity E″ of4.5×10⁷ Pa or less.
 6. The golf ball according to claim 1, wherein thecyclodextrin is an α-cyclodextrin.
 7. The golf ball according to claim1, wherein the linear molecule has a weight average molecular weightranging from 5,000 to 100,000.
 8. The golf ball according to claim 1,wherein (b1) the polyrotaxane has a hydroxyl value ranging from 10mgKOH/g to 400 mgKOH/g.
 9. The golf ball according to claim 1, wherein(b1) the polyrotaxane has a total molecular weight ranging from 30,000to 3,000,000 in a weight average molecular weight.
 10. The golf ballaccording to claim 1, wherein (B) the polyol component further contains(b2) a polyol other than (b1) the polyrotaxane.
 11. The golf ballaccording to claim 10, wherein (b2) the other polyol is at least oneselected from the group consisting of polyoxytetramethylene glycol andbutanediol.
 12. The golf ball according to claim 1, wherein a molarratio (NCO/OH) of an isocyanate group (NCO) in (A) the polyisocyanatecomponent to a hydroxyl group (OH) in (B) the polyol component rangesfrom 0.7 to 1.0.
 13. The golf ball according to claim 10, wherein amolar ratio (NCO/OH) of an isocyanate group (NCO) in (A) thepolyisocyanate component to a hydroxyl group (OH) in (b2) the otherpolyol ranges from 0.8 to 1.2.
 14. The golf ball according to claim 1,wherein the cover composition has a pencil hardness ranging from H to9H.
 15. The golf ball according to claim 1, wherein the covercomposition has a slab hardness ranging from 74 to 94 in Shore Ahardness.
 16. The golf ball according to claim 1, wherein the sphericalcore has a center hardness Ho ranging from 40 to 70 in Shore C hardness.17. The golf ball according to claim 1, wherein the spherical core has asurface hardness Hs ranging from 65 to 100 in Shore C hardness.
 18. Thegolf ball according to claim 1, wherein the spherical core has ahardness difference (Hs−Ho) ranging from 10 to 40 in Shore C hardnessbetween a surface hardness Hs and a center hardness Ho thereof.
 19. Thegolf ball according to claim 1, wherein the linear molecule of (b1) thepolyrotaxane is polyethylene glycol, and the blocking group of (b1) thepolyrotaxane is an adamantyl group, the polyurethane contains (b1) thepolyrotaxane component in an amount of less than 50 mass %, (A) thepolyisocyanate component is 4,4′-dicyclohexylmethane diisocyanate, andthe cover has a loss modulus of elasticity E″ of 4.5×10⁷ Pa or less. 20.The golf ball according to claim 1, wherein (B) the polyol componentfurther contains (b2) a polyol other than (b1) the polyrotaxane, (b2)the other polyol is at least one selected from polyoxytetramethyleneglycol and butanediol, and a molar ratio (NCO/OH) of an isocyanate group(NCO) in (A) the polyisocyanate component to a hydroxyl group (OH) in(b2) the other polyol ranges from 0.8 to 1.2.